The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Fireball Over the Rockies?

On this photo, it appears a fireball is ripping through the late afternoon sky. However, what’s observed here has nothing to do with fireballs or meteors; rather it’s a particularly bright cloud. It was taken looking over the Rocky Mountains in southwestern Alberta, Canada, not far from Calgary, just before sunset on April 23, 2012. This tapered lenticular cloud wasn’t really noteworthy at all until the Sun reached a position 22 degrees to the right of it. The cloud then lit up in spectacular fashion. Essentially, it acted as a stretched out sundog. Ice crystals composing it were oriented just right to refract sunlight through their 60-degree prisms. Sunlight enters through the crystals’ side faces and exits through an alternate side face -- inclined 60 degrees to the one it entered.